As Arabs flee northern Syria, claiming ethnic cleansing by Kurds, reports from the Islamic State stronghold in Raqqa say the caliphate is bracing for a siege.

By David KennerDavid Kenner is the Middle East editor at Foreign Policy. He is based in Beirut, Lebanon, and has been with FP since 2009 (a long time, he knows). He worked for FP previously in Cairo, where he covered the early days of the Arab Spring, and before that in Washington. He has attended Georgetown University and the American University of Beirut and has reported from Libya, Egypt, Gaza, Turkey, Lebanon, and Iraq.

AKCAKALE, Turkey — Syrian Kurdish fighters seized the Syrian border town of Tal Abyad from the Islamic State on Monday, handing the jihadi group a major defeat and cutting off a key supply line to its de facto capital in Raqqa. The battle, however, has also forced thousands of civilians to flee into Turkey and has exposed old fault lines between Kurds and Arab citizens of northern Syria.

Redur Xelil, spokesman for the People’s Protection Units (YPG), the Kurdish militia in the area, confirmed that the town had been captured. Battles still continued in the southern countryside, he said, where an alliance between the YPG and Free Syrian Army-affiliated groups was trying to clear Islamic State fighters from the towns on the road to Raqqa, which lies roughly 60 miles to the south.

“Daesh had a stronghold in the city, but the YPG broke it and killed many of them,” Xelil said, using the Arabic acronym for the Islamic State. “Those who are still alive and can’t go back to Raqqa escaped to Turkey.”

The anti-Islamic State coalition threw its weight behind the offensive in Tal Abyad, devoting almost its entire air campaign in Syria to supporting the forces in the area. Over the last two weeks, it launched 23 airstrikes near Raqqa and 64 airstrikes in the neighboring areas of Hasakah and Kobani, where Kurdish forces advanced from the east and the west, according to U.S. military statements. By comparison, the coalition only launched 14 airstrikes in all other areas of Syria during this time.

The capture of Tal Abyad deprives the Islamic State of a key border crossing with Turkey, from which it smuggled everything from iPhones to bomb-making fertilizer. But for many of the thousands of refugees who crossed into Turkey to flee the fighting, the story is not so simple.

Khodr al-Fadel, a 25-year-old farmer from Syria’s northeastern Hasakah governorate, has spent the past month being chased by war. He was forced to flee west from the fighting when the YPG drove the Islamic State from his home, and he kept on moving until he reached Tal Abyad, where he was squeezed between the jihadi fighters and the Kurdish advance to the east and west. He and thousands of his compatriots camped out on the border with Turkey without food or water for days, while imploring the Turkish military to let them in. After three people died, he said, the Turks eventually relented and let some people in.

It is not the Islamic State, however, but the Kurdish forces who scare Fadel the most.

“We saw them burn houses, burn the crops,” he said. “They just do this to Arabs. The Islamic State didn’t burn our houses or property; they just stole the cars.”

Fadel’s story coincides with reporting that alleges the Kurdish YPG has carried out a campaign of ethnic cleansing in northern Syria with the aim of ridding the area of its Arab population. It is a claim echoed by many of the Arab refugees who crossed into Turkey, as well as by more than a dozen Syrian rebel groups, which released a statement condemning the displacement.

Xelil, the YPG spokesman, vehemently denied the allegations and promised that all civilians would eventually be allowed to return to their homes.

“There is no truth to this, and it’s just a propaganda war paid for by questionable and suspicious groups,” said Xelil. “We ask the media to come to this area to see the truth, and they will know that it is just lies.” So far, restrictions put in place by the Turkish authorities have made it impossible to gain access to the area.

U.S. officials may cheer the Islamic State’s latest defeat, but the Kurdish advance could escalate tensions with Turkey, one of America’s most important allies in the region. The YPG is closely linked with the Kurdistan Workers’ Party (PKK), an insurgent group that fought a bloody 30-year war with the Turkish state. Turkish officials, therefore, are deeply hostile to the growth of an autonomous YPG-controlled area along their border.

“Turkey feels that countering ISIS through military measures, without a political plan [to resolve the entire Syrian conflict], is not helping at all,” said Kadir Ustun, the executive director of the SETA Foundation in Washington, D.C. “It’s simply allowing the various groups to advance their own agenda, and the PYD’s agenda is to secure territory in Syria and forget about the unity of Syria.”

The PYD, or Democratic Union Party, is the political wing of the Kurdish movement and is closely affiliated with the YPG, which serves as its military arm.

For the thousands of new Syrian refugees, however, the international political wrangling matters less than where they are going to get their next meal. Fadel and his family of 10 have been camped out within site of the border crossing for days — not because they are hoping to cross back into Syria, but simply because they have no idea where to go. Food and humanitarian assistance are hard to come by. The Turkish police have at times given them water and chocolate biscuits. The family, along with their 5-year-old child, is sleeping on the trash-strewn ground.

“On the inside, we’re afraid of death and bullets,” Fadel said. “You see what it’s like here: We’re waiting for death, just without the bullets.”